1. Field of the Invention
This invention relates to a process for increasing the melt index and viscosity of polyamide compositions. More particularly, this invention relates to such a process in which the increase in melt index and viscosity is effectuated by the addition of an effective amount of an aryl phosphate compound. Polyamide compositions treated in accordance with the process of this invention are capable of being fabricated into useful shaped articles of manufacture, e.g. filaments, both mono- and multifilament, films, tapes, ribbons, rods, laminates, etc.
2. Description of the Prior Art
Polyamide compositions are disclosed in the prior art as having many and varied uses in industrial and commercial applications. For example, these polymers can be formed in filaments in which the polymer chains are oriented along the filament axis. Such filaments have many uses, in commercial applications as for example in the production of fibers for tire cord, textiles and the like. Similarly, these polymers can be fabricated into other useful shaped articles, as for example, gears, lawn mower housings, skate boards and the like.
The melt index of polyamide compositions provides an indication of the viscosity of the polyamides, and their molecular weights. In general, polymers having low melt indexes are desirable because of improved properties of fibers and other shaped articles made therefrom. For example, fibers made from polymers of relatively low melt indexes have increased tensile strength, durability and impact resistance. These properties are very desirable, especially in fibers used as reinforcement for pneumatic automobile tires.
Several processes have been proposed in the prior art for increasing the viscosity and molecular weight of polyamides, as for example poly(hexamethyleneadipamide). One such method is set forth in U.S. Pat. No. 3,763,113 which discloses a method for increasing the molecular weight of polyamides having recurring --CONH-alkylene-NHCO-alkyleneunits, such as poly(hexamethyleneadipamide) by heating the polyamide with a phosphonic acid derivative in the presence of an inert gas, such as nitrogen. Similarly, U.S. Pat. Nos. 3,551,548 and 3,763,113, each broadly describes a method for increasing the relative viscosity of polyamides, generally, and poly(hexylmethylene adipamide), specifically, by sweeping a molten mixture of the polyamide and phosphorous compound with an inert gas.
Each of these processes provide various adverse effects. For example, in each of the processes an inert gas is employed, which in high concentrations cause uneven finishing, i.e. a variation in the degree of polymerization, throughout the polyamide, which results in a nonuniform polymer. Furthermore, inert gas is expensive, and require additional equipment and monitoring which can increase the cost of commercialization of the process, even though the inert gas is used in small amounts.